1. Field of the Invention
The present invention relates to an upper frame for an excavator which can smoothly transmit the load and shock which is transmitted through a mounting portion of a working device during operation (e.g., a lifting operation mode), to an upper frame by integrally installing a bracket for mounting a fuel tank or the like on an upper plate of the upper frame.
More particularly, the present invention relates to an upper frame for an excavator which can minimize stress concentration due to the load and shock, which is transmitted to an upper frame through a mounting portion of a working device during operation, by integrally extending a bracket for mounting a fuel tank or the like from an upper plate of the upper frame, thereby preventing durability of a welding structure from being deteriorated.
2. Description of the Prior Art
Referring to FIG. 1, a conventional tracked excavator includes a lower driving structure 1, an upper frame 2 swiveled on the lower driving structure 1, an engine room 4 mounted on the upper frame 2 in the rear of the cabin 3, a working device mounted on the upper frame 2 and having a boom 5 driven by a boom cylinder 8, an arm 6 driven by an arm cylinder 9 and a bucket 7 driven by a bucket cylinder 10, and a counter weight 12 mounted in the rear of the upper frame 2 for maintaining a balance of the equipment during operation.
Reference numerals 16 and 17 designate a fuel tank and a hydraulic tank placed in the front of the upper frame 2, respectively.
Referring to FIGS. 1 and 2, the upper frame of the conventional excavator includes a center frame 13 having a bottom plate 13a with a swing ring gear (not shown) mounted on a bottom surface, and a pair of side plates 13b and 13c vertically welded to the bottom plate 13a for supporting the working device comprising the boom 5, a right side frame 14 welded to an outer side of the side plate 13c of the center frame 13 for supporting the fuel tank 16 of the equipment or the like, and a left side frame 15 welded to an outer side of the side plate 13b of the center frame 13 for supporting the cabin 3 or the like.
In this instance, a vibration absorbing device (not shown) is mounted on the left side frame 15 to absorb or relief the shock or vibration transmitted to an interior of the cabin 3 from the lower driving structure 1.
As described above, after the center frame 13, the left side frame 15 and the right side frame 14 are separately manufactured, the left side frame 15 is welded to the side plate 13b of the center frame 13, and the right side frame 14 is welded to the side plate 13c of the center frame 13, thereby completing the upper frame 2.
As shown in FIG. 2, the bracket performing a desired function is mounted at a position adjacent to the welding structure (i.e., the upper plate, the side plate and the lower plate) of the upper frame in order to utilize a limited space in view of characteristics of the equipment.
A bracket 18 is secured to the side plate 13c of the center frame 13 in order to mount the fuel tank 16 and the hydraulic tank at desired positions of the upper frame 2. The bracket 18 is separately secured to the upper plate 19 in opposite to a pair of brackets 20, the working device (i.e., the boom) being pivotally mounted on the brackets 20.
With the above construction, when the shock and load generated during the operation is transmitted to the upper frame 2 through the working device, the shock or the load is not transmitted to the upper frame 2, as the bracket 18 is separated from the upper plate 19.
Also, since the bracket 18 is provided discontinuously from an end of the upper plate 19 (i.e., a gap is formed between the upper plate 19 and the bracket 18), the stress resulted from the shock and load is concentrated on the portion to cause the welded structure to damage or the durability of the upper frame to deteriorate, thereby shortening a lifespan of the equipment.